1. Field of the Invention
The invention relates to a position sensor and a variable capacitor assembly of the position sensor, and more particularly to the position sensor and the variable capacitor assembly that can realize changes of the area covered by the dielectric coupling element at two more electrode plates so as further to alter the fringing capacitance thereof.
2. Description of the Prior Art
Generally speaking, a conventional potentiometer applies mainly a variable resistor to detect a displacement. However, the service life of such a resistor-type potentiometer is usually reduced by the wear at the carbon of the resistor. Hence, another technique for detecting the displacement is to apply the capacitance effect.
Referring to FIG. 1, the capacitance effect between two electrode plates in the art is schematically shown. In an ordinary circuit layout, the capacitor is usually seen as one of basic electronic components. The capacitance effect of the capacitor is induced by the potential difference between the two electrode plates PA1 and PA2. When the two electrode plates PA1 and PA2 are parallel, a parallel capacitance field PEF would be formed between the two parallel electrode plates PA1 and PA2. Meanwhile, at the back and lateral sides of the two respective electrode plates PA1 and PA2, a fringing capacitance field FEF would be formed.
Referring to FIG. 2, a schematic view showing the work theory of a conventional area-varying capacitance sensor is provided. As shown, when the electrode plate PA1 maintains stationary and the electrode plate PA2 displaces horizontally along a parallel direction P1 with respect to the electrode plate PA1, then it is obvious that the covering area of the electrode plate PA2 upon the electrode plate PA1 would vary as well. Namely, the overlapping area of these two electrode plates PA1 and PA2 is varied according to the movement in between. Based on the relative movement, equally the change of the overlapping area, the parallel capacitance field PEF and the fringing capacitance field FEF induced by these two electrode plates PA1 and PA2 would vary as well.
Referring to FIG. 3, changes of the capacitance value with respect to the horizontal displacement for the conventional area-varying capacitance sensor of FIG. 2 are plotted. As shown, since an electric field would be induced by the potential difference between these two electrode plates, thus, in the art, a conductive metal such as a copper is usually applied as a material to produce the electrode plate. In considering the area-varying capacitance sensor, two copper electrode plates can be firstly at a separate state (displacement is 0%), then shift horizontally to become a state of completely overlapping (displacement is 50%), and shift horizontally further to become another separate state (displacement is 100%). The changes in the capacitance values between these two copper electrode plates are plotted in FIG. 3. as shown in FIG. 3, changes for these two conductive metal plates are not significant.
As described above, since relative movement between these two metallic electrode plates won't cause significant changes in the capacitance value, thus, by applying the technique of parallel capacitance effect to the displacement sensor, the sensitivity of the displacement detection via the change in capacitance is poor, and thus can't used as a tool to perform precise control.